1. Field of the Invention
This invention relates to a tool changer for a machine tool which changes tools between a spindle mounted on a spindle head of the machine tool and a tool magazine provided with a plurality of tools.
2. Description of the Related Art
Conventional tool changers include those of the finger type and those of the transfer type. The tool changer of the finger type comprises a changing head rotatable and vertically movable. The changing head is provided with two pairs of opposed gripping claws each pair serving as a holding mechanism for holding a tool. Each pair of gripping claws are driven by a cam mechanism etc. to be opened and closed.
The tool changer of the finger type executes a tool changing operation in the following manner. First, a subsequently used tool is located at a standby position in a tool magazine. A tool currently attached to a spindle of a spindle head is gripped by one pair of gripping claws, whereas the tool located at the standby position is gripped by the other pair of gripping claws. The changing head is then moved downward so that the tools are pulled out of the spindle and the tool magazine respectively. The changing head is then rotated 180 degrees horizontally so that the positions of the tools are changed to each other. Thereafter, the changing head is moved upward so that the subsequently used tool is attached to the spindle, whereas the last used tool is returned to the tool magazine. Each pair of gripping claws are released from the gripping state, whereby the tool changing operation is completed.
According to the tool changer of the finger type, the changing head is rotated 180 degrees in one direction in every tool changing operation. This simplifies the mechanical construction of the tool changer for the control of rotation of the changing head. However, the gripping claws are used in the holding mechanism to detachably hold the tool. The gripping claws require a complicated opening and closing mechanism for opening and closing the gripping claws by means of the cam mechanism etc. Furthermore, the operations of the mechanism for opening and closing the gripping claws need to be synchronized with the rotation and the axial movement of the changing head. Consequently, the manufacturing cost of the tool changer is increased, and a high speed changing operation cannot be attained by the tool changer of the finger type.
On the other hand, the tool changer of the transfer type comprises a pivot arm normally and reversibly rotatable about a pivot and vertically movable. Two holding mechanisms are provided on both ends of the pivot and have moving pins axially urged by springs respectively.
The tool changer of the transfer type executes a tool changing operation in the following manner. First, a subsequently used tool is located at a standby position in a tool magazine. The pivot arm is located at a change standby position. The pivot arm is then rotated by an angle of .theta. in the reverse direction so that a tool currently attached to a spindle of a spindle head and the tool located at the standby position are gripped by the holding mechanisms provided on both ends of the pivot arm respectively. The pivot arm is then moved downward so that the tools are pulled out of the spindle and the tool magazine respectively. The pivot arm is then rotated 180 degrees in the normal direction so that the positions of the tools are changed to each other. The pivot arm is then moved upward so that the subsequently used tool is attached to the spindle, whereas the last used tool is returned to the tool magazine. Thereafter, the pivot arm is further rotated by the angle of in the normal direction to be returned to the change standby position, and each holding mechanism is released from the holding state.
According to the tool changer of the transfer type, the moving pins are urged by the respective springs in each holding mechanism thereof. Thus, since each holding mechanism has a simple construction, the manufacturing cost thereof can be reduced. Furthermore, a complicated control is not required for each holding mechanism. However, the pivot arm requires to be rotated in the normal and reverse directions in every tool changing operation. Furthermore, the pivot arm requires the two rotation angles of .theta. and 180 degrees. These requirements complicate the mechanical construction for the control of rotation of the pivot arm.